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Account of the self-interaction energy correction in the first principles calculation of the fundamental absorption edge spectrum of LiCl

M. A. Bunin, I. I Geguzin

TL;DR

This work addresses the poor description of optical spectra near the fundamental edge in wide-bandgap dielectrics within standard LDA-DFT by introducing a muffin-tin self-interaction correction (MT-SIC) that enforces electroneutrality. The method partitions the unit cell and subtracts self-interaction within the SIC region to yield a self-consistent potential, enabling first-principles calculation of optical spectra using basisless approaches like KKR or APW. Applied to LiCl, SIC primarily shifts energy levels and modulates interband matrix elements, yielding a fundamental gap closer to experiment and an absorption spectrum that aligns with experiment away from the edge, while near-edge features require electron-hole (hole) corrections and exciton considerations. The results demonstrate that incorporating SIC improves spectral agreement without ad hoc energy-scale adjustments and offers a practical route to interpret and predict the optical response of wide-bandgap dielectrics. The approach thus provides a physically motivated, transferable framework for first-principles optical spectroscopy in ionic crystals.

Abstract

Within the framework of the local electron density functional theory, an ab-initio method is proposed that takes into account the self-interaction energy correction (SIC) for the crystal potential. The principle of dividing the unit cell into regions remained the same as for the ground-state potential. The expression for the self-consistent muffin-tin-SIC potential satisfies the condition of cell electroneutrality. This scheme was applied to calculate the spectrum of the fundamental absorption edge of LiCl. The obtained interband transition energies were not required for fitting to experimental values. In the calculated spectrum, the shape and position of the peaks above ~2.5 eV from the edge agree fairly well with the measured ones, which allows their intensity in this region to be attributed primarily to interband transitions. Closer to the edge, electron-hole interaction significantly alters the ground state, which must be taken into account when calculating the spectrum shape.

Account of the self-interaction energy correction in the first principles calculation of the fundamental absorption edge spectrum of LiCl

TL;DR

This work addresses the poor description of optical spectra near the fundamental edge in wide-bandgap dielectrics within standard LDA-DFT by introducing a muffin-tin self-interaction correction (MT-SIC) that enforces electroneutrality. The method partitions the unit cell and subtracts self-interaction within the SIC region to yield a self-consistent potential, enabling first-principles calculation of optical spectra using basisless approaches like KKR or APW. Applied to LiCl, SIC primarily shifts energy levels and modulates interband matrix elements, yielding a fundamental gap closer to experiment and an absorption spectrum that aligns with experiment away from the edge, while near-edge features require electron-hole (hole) corrections and exciton considerations. The results demonstrate that incorporating SIC improves spectral agreement without ad hoc energy-scale adjustments and offers a practical route to interpret and predict the optical response of wide-bandgap dielectrics. The approach thus provides a physically motivated, transferable framework for first-principles optical spectroscopy in ionic crystals.

Abstract

Within the framework of the local electron density functional theory, an ab-initio method is proposed that takes into account the self-interaction energy correction (SIC) for the crystal potential. The principle of dividing the unit cell into regions remained the same as for the ground-state potential. The expression for the self-consistent muffin-tin-SIC potential satisfies the condition of cell electroneutrality. This scheme was applied to calculate the spectrum of the fundamental absorption edge of LiCl. The obtained interband transition energies were not required for fitting to experimental values. In the calculated spectrum, the shape and position of the peaks above ~2.5 eV from the edge agree fairly well with the measured ones, which allows their intensity in this region to be attributed primarily to interband transitions. Closer to the edge, electron-hole interaction significantly alters the ground state, which must be taken into account when calculating the spectrum shape.
Paper Structure (5 sections, 7 equations, 3 figures, 2 tables)

This paper contains 5 sections, 7 equations, 3 figures, 2 tables.

Table of Contents

  1. Introduction
  2. MT-SIC potential
  3. The influence of self-interaction on the electronic structure of LiCl
  4. Fundamental absorption edge of LiCl
  5. Conclusion

Figures (3)

  • Figure 1: Partitioning of the unit cell space $\Omega$: $(1)=\Omega_{\textit{s}}^{\textit{sic}}$; $(2)=\Omega_{II}^{\textit{mt}}$; $(1)+(3)=\Omega_{\textit{s}}^{\textit{mt}}$; $\Omega_{I}^{\textit{sic}}=\sum_{s}\Omega_{s}^{\textit{sic}}$, $\Omega_{I}^{\textit{mt}}=\sum_{s}\Omega_{s}^{\textit{mt}}$
  • Figure 2: Local densities of states for chlorine atom in LiCl, calculated for $\textit{a}_{1g}$ (lower part) and $\textit{e}_{g}$ (upper part) states for SIC (solid line) and GS approaches (dashed line). Zero on the energy scale corresponds to the conduction band bottom.
  • Figure 3: (a)- The fundamental absorption edge spectrum $\mu(\omega)$ for LiCl: 1$-$ experimental spectrum from [3], 2$-$ SIC calculation, 3 $-$ GS calculation.